This invention relates to a method for lowering the concentration of trace contaminants in a liquid to lower concentrations tantamount to substantially complete removal of the trace contaminants. It also relates to a unique apparatus suitable for use in conjunction with the method. In a preferred aspect, the method and apparatus can be applied to the removal of trace radioactive contaminants from effluent streams.
There are many instances wherein trace contamination must be tolerated because there is no satisfactory method for removing such low concentrations both from the viewpoint of cost and effectiveness. It has generally not been possible to apply methods for removing larger concentrations of the same chemical components from liquid systems. Despite the large scope of prior art on insolubilizing chemical components in order to separate them from a liquid system, there is a relative paucity of techniques which can be applied in practice to the removal of the same chemical components when present as trace contaminants in the same or other liquid systems.
For example, it is known to remove cobalt from solutions by various oxidation techniques, often using oxidizing agents such as hypochlorite (U.S. Pat. Nos. 1,365,358 or 3,203,786), nickelic oxide (U.S. Pat. Nos. 2,377,832 or 2,726,144), etc. It is also known to prepare nickel black, i.e., remove nickel from a nickeliferous solution using the strong oxidizing agent resulting from the combination of a sulfite, e.g., calcium sulfite, and oxygen gas. See, e.g., U.S. Pat. No. 4,006,216 and Devuyst et al, Chemtech, July 1979, pp 426-427. Many other references discuss the use of the same or similar oxidizing agents to remove various oxidizable chemical components from liquid systems. See, e.g., Chemical Abstracts, 93:119835m; 92:28189s; 91:96203w; 91:7108d; 87:25437g; 84:34854m; 77:105397c; 84:126479r; 89:152107r.
All of these references have in common the fact that all involve the removal of relatively large amounts of the chemical component of interest from the respective liquid system. In general, these references are drawn to the recovery of the desired component from the system rather than the decontamination of the system. Since there is no expectation that a chemical method for recovering relatively large amounts of a chemical component can be applied to the decontamination of other systems contaminated by that component, in essence, the cited references and others of their ilk are of no help in solving the problem at hand, viz., the decontamination of systems contaminated by trace amounts of chemical constituents.
Of course, there are references which relate to decontamination methods per se. However, by and large, these also deal with achieving final contaminant amounts which exceed even the beginning contaminant concentration existing in many of the systems treated by this invention. For example, U.S. Pat. No. 4,221,766 discloses a relatively simple method for removing ferrous ions from an effluent stream by O.sub.2 oxidation thereof to the ferric state. In this method, final contaminant concentrations are about 5 ppm.
There still exists a significant need for a method which enables the decontamination of liquid systems containing trace amounts of contaminants, preferably a method by which many known chemical reactions can be applied to the problem.